Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.59   8.606%   $226.5413   $226.54   $226.55   $226.50  
  Purchase #2 $52.54   4.375%   $54.8386   $54.84   $54.85   $54.80  
  Purchase #3 $42.94   12.137%   $48.1516   $48.15   $48.15   $48.20  
  Purchase #4 $129.38   4.806%   $135.598   $135.60   $135.60   $135.60  
  Purchase #5 $197.29   8.326%   $213.7164   $213.72   $213.70   $213.70  
  Purchase #6 $103.65   7.140%   $111.0506   $111.05   $111.05   $111.10  
  Purchase #7 $98.36   5.578%   $103.8465   $103.85   $103.85   $103.80  
  7 purchase totals = $832.75       $893.7430   $893.75   $893.75   $893.70